Method of and apparatus for radiating sound waves



R. D. FAY ET AL.

June 26, 1928.,

METHOD OF AND APPARATUS FOR RADIATING SOUND WAVES Filed April 17, 1925 5 Sheets-Sheet l W Z @mdmi? June 26 X923,

R. D. FAY ET AL METHOD OF AND APPARATUS FOR RADIATING SOUND WAVES 5 Sheets-Sheet 2 Filed June 26, 19280 1,674,895

R. D. FAY ET AL METHOD OF AND APPARATUfS FOR RADIATING SOUND WAVES Filed April 17, 1925 5 Sheets-Sheet 3 FT 6'. E M

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R. D. FAY ET AL METHOD OF AND APPARATUS FOR RADIATING SOUND WAVES Filed April 1'7, 1925 5 Sheets-Sheet June 26 19285 R. D. FAY ET AL METHOD OF AND APPARATUS FOR RADIATING- SOUND WAVES Filed April 17, 1925 5 Sheets-Sheet isa Patented dune 12$, 1928,

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HE'LHOD OF AND APPARATUS FOR, EADIATING SOUND 'WAVEfl Application filed April 17, 1925. :Ssrial No. 23,917..

Our invention relates to a method of and an apparatus for radiating sound waves, and

apted particularly for use with radiophone receiving systems, although capable of more general application and not limited to such use.

It is well knownlthat electromagneticallyoperated sound-radiating devices commonly known as loud speakers that employ dia hragms, sound chambers and horns are sub ect to certain limitations chief of which is their inability to reproduce the sounds initiated at the transmitting station without change of pitch and timbre or quality,-the main cause of such distortion being the impossibility of eliminating the natural period of the diaphragm and the stationary parts associated therewith. Another-limitation to which such devices are subject is the. absorption of ener by the stationary parts asso ciated with t e diaphragm or other vibrating member and the resulting creation'of mechanical vibrations in such parts with the result that, for a given amount-of receivedenergy-,the amplitude of the sound Waves emitted-is reduced. While loud speakers employing sound radiating members such as plates and cones constructed and arranged to propagate relatively-intense sound waves through. the air are in certain respects more satisfactory than those of the diaphragm and horn type and reproduce sounds more faithfully over' a somewhat wider range of'frequencies, they do not, so far as we are advised, overcome such objections as the undue amplification of sound waves havin a pitch approximately equal to the natur period of the vibrating system, the wasting of energy by'thecrpation of vibrations in parts intended to be stationary, and the inability to reproduce notes of the lower frequencies unless the area of the radiating member is rohibitively large.

The principal object of our invention, generically speaking, is to provide a method of and an apparatusfor-the radiation of sound waves of a wider range of freq'uenciesthan has heretofore been found possible without unduly increasing the linear dimensionsof the sound-radiating member or members, the greatest linear dimension of our device being only about one-thirty-seventh of the wave length in air of the lowest tone to be reproduced, and for the more faithful and efficient reproduction of the quality and pitch of the original sounds'than can'be effected by the prior methods and apparatus.

A special object of our invention-is to 'pro-. vide a sound-radiating device in which the entire vibrating system is balanced, the force acting on any element of the system being balanced by an equal and opposite force on the counterpart of. such e 1 11 17, thereby eliminating the tendency of the elements to set up vibrations in the stationary parts associated therewith and mak- Another object of our-invention is to pro vide a sound-radiating device by means of which'the sound waves produced by the two surfaces'of a sound-radiating member constructed andarrang'ed for the propagation .of relatively intense sound waves throughthe' air will be prevented from interfering; or a sound-radiating device having two such sound-radiating members disposed opposite- 1y by means of which the sound waves produced by the inner surfaces of said members are prevented from interfering with those produced by the outer surfaces thereof.

Another object of our invention is to provide a sound-radiating device in which the sound-radiating member is actuated by one of two oppositely-directed armatures each carried 'by a flexible supporting member togetherwith means for preventing interference between the sound waves produced b the two surfaces of said member; or a soun radiating device in which two'oppositelydisposed sound-radiating members are employed, each-actuated by one of said armatures, together with means for preventing interference between-the sound waves duced by the inner and outer surfaces of said radiating members.

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A further object of our invention is to procenter on its actuating armature; or in which a conical sound-radiating member is supported at its apex on its actuating armature and, preferably, flares outwardly therefrom; orin which two such members oppositely :disposed may beemployed; such soundlid) radiating member preferably being supported solely by its actuating armature.

Another object of. our invention is to provide a, magnetic circuit in which there shall be a maximum change in thegap flux for a given change in gap reluctance in order that the back electromotive force in the energizing winding will be a maximum for any motion of the armatures; and this object more specifically stated is to provide a magnetic circuit formed in part by a permanent magnet having two oppositely-disposed and substantiallyrigid arms each supporting a flexible permeable member, such as a relativelystifl disc, and two oppositely-directed armatures each carried by one of said discs and having their juxtaposed faces separated by a relatively-short air gap, the said circuit being so arranged that the'reluctance of the path through the energizing coil is substan tially equal to the reluctance of the path between the poles of said permanent magnet which does not link said coil.

A further object of our invention is to provide means for adjusting and varying the reluctance of the path through the energizing coil, or means for adjusting and varyin the reluctance of the path between the po es of the permanent magnet, or both, for the purpose of securinga substantial equality between the said reluctances. 7

Various other objects of our invention will hereinafter appear in the detailed description of the several illustrative embodiments of our invention.

With the foregoing objects in view our invention in its broadest aspect comprises a method of converting variable electric currents into radiated sound waves, as distinguished from sound waves produced in a casing or tube adapted to be held to the ear, which consists in superimposing the magnetic flux created by-electric currents modified in accordance with the sound waves initiated at another point upon a constant magnetic flux, such as the flux created by a permanent magnet or the sum of such flux and the flux created by the direct current component of such variable currents without altering the intensity of such constant magnetic flux, then converting the resultant. flux into equal and opposite mechanical motions, thereby eliminatingthe creation of vibrations inthe' stationary parts of the apparatus and efmasses converting one of said "mechanical motions into radiating sound waves; or else converting said mechanical motionsinto two sets of substantial] hemispherically radiating sound waves 0 like pressure phase.'

Our invention comprises also an apparatus for converting variable electric currents into radiated sound waves by subjecting a tympanum to a magnetic force and to a mechanical force which for a given position of said tympanum is equal and opposite to said magnetic force, and maintaining such substantial equality for all positions of said tympanum on either sideof said given position throughout the working range thereof, whereby for the lower audible frequencies a. maximum vibrational amplitude of said tympanum is effected for a given change in said variable flux and 'the mechanical period-of the vibrating system is 'ke t below thelimit of audibility so that, as a ove set forth, the original sounds will be reproduced witlilout substantial change in timbre or pitc In carrying out the foregoing methods our invention contemplates-the use of .two oppositely-disposed armatures supported, re-

spectively, by substantially-parallel flexible matures, together with means for preventing interference between the sound waves .produced by the inner and outersurfaces of said radlating member. It contemplates also such use of two oppositely-disposed sound-radiating members of any appropriate shape, conical or otherwise, each supported at its center on one of the armatures aforesaid, and in the case of conical radiat-' ing members, each cone preferably flares outwardly from its point of support. In either case we prefer to support the soundradiating mem er solely by its actuating armature,

Our invention comprises means whereby the sound waves produced by the two sur faces of a sound-radiating memberconstructed and arranged for the propagation of relativelyintense sound waves through the air will be prevented from interfering. or means whereby the sound waves produced by the inner surfaces of two such sound-radiating members oppositely disposed are prevented from interfering with the sound waves roduced by the outer surfaces there of, suc means consisting in general of an enclosure screening the space between the two surfaces of a single sound-radiating member or the space between the two sets of surfaces where two oppositely-disposed members are employed.

Our invention comprises also a sound-radiating device having two opposltely disposed sound-radiating members constructed and arranged for the propagation through the air of relatively intense sound waves of like pressure phase together with means of part-of two oppositely-directed armatures,

the juxtaposed faces of which are separated by a relatively short gap and "a permanent magnet having two oppositely-disposed and substantially-rigid arms each carrying a flexible permeable member by which said armatures, respectively, are supported, the reluctance of the path through the armature-magnetizing winding being substantially equal to the reluctance between the poles of said magnet which does not link said winding. whereby a maximumchange in the gap flux is obtained for a given change in gap reluctance, this resulting, in a maximum back electromotive force in said winding for any motion of the'armatures; and it comprises also means for adjusting and equalizing the reluctance of either or both of said paths. I I

Our invention comprises various parts and combinations of parts hereinafter more fully described and set forth in the appended claims.

In the drawings which accompany and form a part of this specification we have shown in detail various embodiments of our invention which have given good results in practice and also several modifications thereof; but .these constructions are to be considered as illustrative rather than restrictive, because the principle underlying our invention may be embodied in a variety of apparatus while the methods hereinbeforereferred to are broader than mere apparatus and may be realized in practice by a variety of mechanical and electrical expedients.

In said drawings- Figure 1 is a front elevation of a soundradiating device embodying our invention and by means of which our methodmay be carried intoeffect; Y

Fig. 2 is a front elevation with one of the sound-radiating members removed, the enclosing casing being shown in verticaLsection;

Fig taken on the line 33 of Fig. 4-;

. 3 is a vertical longitudinal section Fig. 4: is a vertical transverse section taken on the line 44 of Fig. 3;

Fig. 5 is a section on an enlarged scale corresponding to Fig. 4;

Fig. 6 is a front elevation of a modification with one of the sound-radiating members removed and the casing shown in section, said figure illustrating an alternative means for varying the'leakage reluctance.

Fig. 7 is a horizontal sectiontaken on th line 7- 7 of Fig. 6;.

F ig. 8*is a side elevation of a sound-radiating device in which no permanent mag-- net is employed;

Fig. .9 is a vertical section tak n on the line 99 of Fig. 8;

Fig. 1.0 is a side elevation of a further modification in whichcantilever springs are employed for supporting the armatures;

Fig-11 is a front view of the construction illustrated in Fig. 10;

Fig. 12 is a front View of a modification of the construction shown in Fig. 10;

Fig. 13 'is a horizontal section of another modification in which the armatures are supported.,by flatsprings;

Fig. 14 is a front elevation of ratus shown in Fig. 13;

Fig. 15 is a vertical section taken on the line 1515 of Fig. 13;

Fig. 16 is a plan view of a perforated armature-s11 porting diaphragm;

Fig. 17 1s a section taken on the line 17- -17 of Fig. 16;

Fig. 18 is a plan view of a modification in, which a spider is employed for supporting the armatures;

Fig. 19 is a section taken on the line 19-19 of Fig. 18;

Fig. 20 is a the appahorizontal section of a' soundradiating device in which only one radiating member is employed;

Fig. 21 is a longitudinal central section of a cone by means of which there are radiating sound waves having wave fronts that are .initially plane;

Fig. 22 is a longitudinal central section of a cone by means of which there are ra material which in turn is bolted to the base l tively stiff flexible discs each'clamped be- .of the casing 27, although it will be understood of course that we may employ a onepiece permanent magnet of the U- or horse-' shoeshape, orof any other suitable shape.

Secured to the inner sides of said arms near the upper ends thereof are two oppositelydisposed and substantially-parallel flexible permeable armature-supporting members 28, 28 whichin that embodiment of our invention shown in Figs. 1 to 7, inclusive, are relatween-a pair of permeable rings.29, 29, -ar.-'

' ranged on the opposite faces of each disc;

near the; periphery thereof, by screws or bolts 30. In the present instance the discs are secured to the permanent magnet by to the permanent magnet.

bolts 31 which assist in clamping the disc's between their respective-supporting rings.

The bolt 32 6f non-permeable metal and the nuts 33 threaded thereon'serve not only to clamp the discs between the rings 29, but also to hold said discs rigidly spaced apart at the portion of their circumferences farthest away from their'points of attachment Two oppositely-directed armatures herein shownas tubular are supported on said discs respectively atthe centers thereof, and in the present instance each armature is shown as having a threaded end pro'ecting through its supportingdisc 'on w ich ends nuts 35 are threadedto clamp the disc between said-nut and a shoulder 36 on the armature. It will be understood of course thatanytsuitable means may beexn'ployed for securing said armaturesto the discs.

Supported by the armatures'in any suit able manner-are oppositely-disposed soundradiating members37, 38 which maybe of 1 parchment, fibre or any other suitable ma-,

terial, and preferablythe said sound-radiating members-if conical as shown have their peripheral portions slightly bent back. as shown at 39. It will be understood of course that the said sound-radiating members, each of which is supported at its center on one of said armatures,- are not necessarily conical. In the present nstance each conical tympanum orsound-radiating member is supported solely atitsapex on its actuating ar-' mature by meansof a-sleeve 40 which passes through the apex. and is threaded to the outwardly projecting end of the'armature,

said sleeve being formed integral with a I with the armatures, said coil being wound on an insulating spool e3 supported in the Lewtsea present instance in. the rabbeted inner peripheries ofthe adjacent rings 29. In order to avoid the possible detrimental'eflects of air compression in the space between the spool and the discs,the inner rings 29may be rovided'with a series of holes 44. a he juxtaposed faces of y the armat'gres "which are separated by a relatively short gap are plane and are normal to the common axis ofthe two armatures so that they are in absolute parallelism, and in our preferred construction the said armatures are slotted longitudinally to" eliminate eddy current losses as shown at 45.

When the magnetizing coil 42 is energized by currents modified in accordance with.

sound waves initiated at another point as for example the variable undirectional currents in the plate circuit ofa radiophonereceiving system to which said coil may be electrically connected bythe leads 4:6,or by variable elec tric currents of' any nature, the constant magnetic flux in the air gap between the armatures created by the permanent magnet will be modifiedand hence the magnetic pull on the armatures will bechanged, and as the same force acts'on each armature in opposite directions, the motions of said armatures will be equal and opposite, thereby causing the outer surfaces ofthe cones to produce sound waves'of like'pressure phase and-the inner surfaces'thereof to produce sound waves of like pressure phaseopposite to thatiof the phase of the soundsproduced by said-outer surfaces. It will be noted that a force acting on any element of the system is balanced by an equal and opposite force on the'counterpart of such element so'that the tendency of the moving elements to create mechanical vibrations in their associated stationary parts is eliminatedand practically all of the energy of motion is converted into-sound .waves. This' saving of energy is especially important in the reproduction of the lower frequencies and we have succ eededby our invention in reproducing the lowest audible notes with substantially the same facility as those of the upper register by using soundradiating cones whose diameter is about twelve inches or approximately one thirtyseventh of the wave length in air of the sound made by the lower notes of apiano, say, about thirty cycles 'per'second.

In order'to reproduce sounds of low pitch the radiating member must have a comparativel large area because the radiation depen s on the square of the area or on the fourth power of the radius if thetympanum is circular, when the radius of the surface is small with respect to the wave length of the int sound, provided however that the sound waves'produced by'the' opposite surfaces of the sound-radiating member are prevented from interfering with each other. In the absenceof such means for preventing interincrease ference practically no radiation can be ef-' the present, instance our sound-radiating Ill) members would have to be about 220" in diameter in order to radiate waves having a.

frequency of thirty .per second unless such interference was prevented.

We therefore provide means for preventin'g interference between the sound Waves produced by the inner and outer surfaces of the cones 37 38, or in the case where a single cone or sound-radiating 'member of other shape is employed as illustrated in F ig.' 20, means for preventin' interference between the soundwaves pro need. by the inner and v outer surfaces of the single sound-radiating member. Such prevention of interference -may be accomplished in a variety of ways,

and in the present instance we have illus trated the arrangement which we prefer to use for this purpose, viz, a casing 27 which suficiently encloses andscreens the space between the inner surfaces of said members to prevent the sound Waves produced by said inner surfaces from interfering with the sound waves produced bythe outer surfaces thereof. Inasmuch as the outer surfaces of the cones create sound waves of like pressure phase and interference between said waves and those produced by the inner surfaces is prevented, we obtain substantially the same reinforcing effect as if' a rigid medial plane through which sound waves could not pass were placed between the cones normal to the axis of the armatures, and also a hemispherical, rather than a spherical, sound-wavedistributiori whichresults in the doubling of the radiation resistance for each side, in other words, the area-of each surface may be halved Without reducing the radiation resistance.

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The electromagnetic mechanism employed to vibratea radiating surface must operate efiectively with less amplitude and wlthlarger force than the mechanism employed to actuate the diaphragm of a loud speaker of the horn type, and therefore some form of lever is usually employed to couple a radiating surface to its actuating mechanism. We have found, however, that such lever connect-ion unnecessary in our improved sound-radiating device, for Webbtain by electromagnetic means the virtual equivalent of a mechanicallever increasing the actuating force on the radiating surface. We thereby eliminate unnecessary weight in the moving parts because the smaller radiators which We are able to use may be made of lighter material than those of larger size heretofore found necessary, there is no weight required or mechanical levers and as the .arma-tures have the same amplitude as the radiating members, the effect of their weight is not increased as it would be if mechanical levers were necessary, It is well understoo of course that for reproduction of sound aves of the higher frequenthe vibrating members must be as light as feasible, and therefore it will be seen that the elimination of unnecessary weight the. relative travel of the moving parts 1s doubled and the weight thereof is reduced.

It will of course readily occur to those skilled in the art that a further reduction in the weight of'the moving parts may be effected by shortening the armatures and introducing a fixed core in the gap between their proximate faces, but this arrangement has certain disadvantages, viz, there are two gaps tomaintain in close adjustment, there is an increased magnetic leakage, and the magnetomotive force at' the gaps is reduced because obviously neither gap can be at the center of the coil and while We'consider this arrangement within the scope of our invention, we nevertheless prefer to use two armatures separated by a single gap and to. obtain any desirable further reduction in weight by shortening the armatures and employing a narrower or flatter coil.

One of the most important features of our invention, the maintaining of the mechanical period of the vibrating system below the limit of audibility so that the original sounds will be reproduced without substantial change in quality or pitch, is accomplished in the following manner: The discs 28, 28. are'so designed as to size, stiffness,

any

elasticity and mode of support that for a given length of gap between the armatures,

say 0005" or for a given position of the tympanum, the force exerted on said armatures by the resultant of the flux of the permanent magnet and the flux created the direct current component of the variable currents energizing the coil is equal and opposite to the mechanical force exerted thereon by said discs, and substantially such equality is maintained throughoutthe working range of the apparatus, that is,'for gaps slightly longer and gaps slightly shorter than said given gap and consequently for all positions of the tympanum on either side of said given position, whereby for the lower audible frequencies a maximum change in the length of said gap and a maximum vibrational amplitude of said tympanum is effected for a given change in the amplitude of the variable component of said variable electric currents or for a given change in said magnetic flux. When the several parts are constructed and arranged in the manner aforesaid we have found that sounds are reproduced without distortion and that notes of the lowest audible frequency which are absent in the reproduction efiected' by the loudspeakers of the prior art are emitted with the same fidelity as those of the upper register.

The equilibrium above mentioned may be demonstrated by de-energizing the winding 42am]. adjusting the screw 47 the function of which is hereinafter more fully described until the gap. between the armatures is as short as the normally-unflexed discs and the normal positions of the arms of the permanent magnet will permit, and then energizing said coilby direct current having a value of the order of that of the current flowing in the plate circuit of the usual radiophone receiving system. The vibrating system will then immediatelyspring into a positionof equilibrium, the armatures moving in opposite directions against the retractile force of the discs and reducing the length of the gap. It will then be found that a very slight pressure exerted by the fingers on the discs will suflice to close the gap, but if the winding is de-energized by disconnecting the same from the plate circuit it will be difiicult to exert sllificient presthat for a gap length of 0.005 ','in this par- I ticular example, the ordinates of the curves 0. and b are equal and opposite which means of course that the vibrating system is in equilibrium. 'The curve 0 which represents the algebraic sum of the curves a. and b crosses the zero axis at 0.005, of course, and is negative for shorter gap lengths and positive. for longer gap lengths. The normal magnetic force tending to close the gap 'is a function of the permanent magnetic flux and the: flux created by the direct current component of the variable electric currents energizingthe coil. When the radipphone receiving system is in operation" and a uni-directional pulsatory current is created in the plate circuit thereof, the variable component of such'current flowing through the coil 42-increases themagnetic pull tending to close the gap, and in such case the dotted ine curve 03 represents the variation of the total magnetic flux acting on the armatures while the dotted line curve e will then represent'the effective pull on the armatures, that isto say, the difference between the total magnetic pull tending to close the gap and the restoring mechanical force of the discs. -In the case assumed the'dotted line masses curve e crosses the zero axis at 0.0025" and. at that point the vibrating system is'in equilibrium at the instant the ordinates of the curve I) and d are equal and opposite. It

will be understood of course that the curve d is constantlyvarying and that the point at which'the curve 6 crosses the zero axis is changing continually, and careful consideration of Fig. 23 will show that the two opposing forces acting on the armature are substantially equal and opposite throughout 7 the working range of the apparatus.

In order to increase the eficiency of ourimproved sound radiating device for use with high radiation damping, we prefer to so arrange matters that the magnetiereluc tance of the path through the energizing coil is substantially equal to the magnetic reluctance of the path between the poles of the permanent magnet which does not link said coil, and provide means for adjusting and varying the reluctance of either or both of saidpaths.

The total magnetic flux through the midpoint of a permanent magnet is not efiected by the reluctance of the path between its poles, changes in'reluctance altering the distribution of. the flux but not the amount. There are two paths for the flux, one through the armatures 34, 34, and air gap, this path linking the winding 42, and the other comprises all leakage paths outside said winding, such as the paths between the two arms 25, 25, the outer portions of the disc 28, 28,

a the clamping rings 29, 29, etc., .the flux dividing inversely as the reluctances of the two paths. 7 The flux through the gap is given by =r a, f (H 1);

where R is the gap reluctance, B is the leakage reluctance and F is the total flux, the equation containing onl two variables f andR In order that t e back electromotive force in the winding 42 will be a maximum for any motion of the armatures 34, 34, we may determine values for]? and B which make a maximum'when f is as great as possible without saturating the iron in the armatures.

The gap flux f is essentially a variable depending luctance which is a function of. and while the best value for f Wlll have to be determined empirically we. have found that the limiting value'thereoffor good operation is such that will be just suflicient to saturate the armatures as much as .is desirable when the gap is closed.

among other things-on the gap regap length.

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' newest We have ascertained experimentallythat the maximum effect occurs when the leakage reluctance is approximately equal to the average gap reluctance in which case 7 is equal to F. When this relation obtains a' given change in magnetic flux produces a maximum pull on the armatures for a gap of given length.

In order to secure and maintain the substantial equality of the gap reluctance and the leakage reluctance as aforesaid, we provide a leakage path chiefly through the air,-

so as not to introduce iron losses, which has a reluctance approximately equal to that of the gap, and we provide also means for adjusting one or both of said reluctances. Preferably the permanent magnet has a flux about double that required to saturate the armatures,--=about one-half of said flux passing through the armatures and one-half passing outside" the same, and the armature supporting discs 'and the pole pieces of said luctances when the device is in operation in order toget the best response.

@ne very simple means for adjusting said reluctances consists in the screw 47 threaded through one of the arms of the permanent magnet and having its end bearing against the other arm whereby the poles of the magnet may be sprung and the armatures 34, 34, separated. The separationof said armatures will of course increase the reluctance of the air gap and to a slight and almost inappreciable degree the leakage reluctance also.

Another means for maintaining the aforesaid relation between the two reluctances'is illustrated in Figs. 6 and 7 in which an iron segment 48 carried by the rod 49 threaded I into the bushing 50 and terminating in the ing said gap and hence increasing its'reluctance, while at the same time the reluctance of the leakage path is reduced. It is tobe understood however that we do not [limit ourselves to either of the arrangements described for varying the reluctance of either of said paths inasmuch as a variety of equivalent means will readily occur to those skilled in the art.

Our sound-radiating device is operative without the permanent magnet 25, 25, when the operating current is uni-directional as for example the current in the output circuit of a vacuum tube, and an embodiment of our invention which does not employ such 'permanentmagnet is shown in Figs. 8 and 9 in which the rings 29, 29 are directly connected to each other by permeable members 52, 52, the device in such case being supported in the casing 27. by any suitable means and its operation being substantially as above set forth in connection with Figs. 1 to 5 inclusive.

In Figs. 10 and 11 cantilever springs 53 attached to the poles of the permanent magnet 54 take theplace of the discs. 28, 28 as armature-supporting members, the winding 55 enclosing the armatures as above set forth in connection with the winding 42. In Fig. 12 we show an alternative means for magnetizing the armatures', a winding 56 in such case being disposed around one or both of the cantilever springs 53. WTe prefer how ever to employ windings of the type shown I in the other figures in which the gap between the. armat-ures is at the center of the coil.

Another modification is shown in Figs. 13, 14 and 15 in which the armatures 34, 34 are supported on the thin plate springs 57 57 bolted at their ends to the transverselyextending pole pieces 58, 58, of the per- .manent magnet 25. In this construction the flanges 59 of the spool on which the coil 42 is wound are extended as shown and supported by the ends of the bolts 60 whereby the springs 57 are attached to the magnet pole pieces.

The modifications shown in Figs. 16 to 19 inclusive illustrate constructions by which the weight of the vibrating system may be reduced. In Figs. 16 and 17 the diaphragm 61 is perforated as shown at 62, 62. In Figs. 18 and 19 a four-armed spider 63 is employed for supporting each armature. In both cases and in constructions where other forms of armature-supporting members are used, the same considerations set forth above in connection with the detailed description of Figs. 1 to 5 inclusive apply.

We have found that it is not essential to employ two oppositely-disposed sound-radiating, members and that good results are obtained by omitting one such member but retaining the vibrating system otherwise intact. I

Fig. 20 shows a sound-radiating device embodying our invention that is particularly designed for incorporation in the cabinet of a radio-receiving'set. In this construction the free armature is found to react on the armature which supports the sound-radiating member 37 and to reinforce its action.

The nut 35 whereby the free armature is 'clamped to one of the discs 28 may be slightly larger than the corresponding nut shownin Fig. for securing the other armature to the other disc, if thelatter nut be employed. or as shown in F ig. the threaded sleeve may serve'to clampthe cone supporting armature-to-its disc. Ineither case the weight of said nut'on the free armature will serve in a certain degree to compensate for the reduction of Weight resulting from the .omission of the, cone 38. There is evidently a magnetic coupling between the armatures which tends to balance the two sides of the vibrating system;

sarily accurately parallel.

the discs are clamped between their rings 29 until the mandrel can be'removed'without effort,- in which case the juxtaposed faces of i the oppositely-directed armatures are neces- While wehave shown the discs 28 provided with a series of perforations 44, it is possible to use solid'or unperforated diaphragms as supports and to closethe bores of the out- In the cone 64 shown in section in Fig.

the height is siichthat sound waves radiated therefrom will reach the plane of the base atthe same time that such waves traveling through the material of the cone from the apex 65 reach the outer periphery 66 so that the wave front is initially'plane, the dotted lines 67, 67 indicating the successive positions of the wave fronts of the radiated waves. The dotted lines 68,,68 indicate ap-.

proximately the wave frontsiof the waves radiated from the inner surface of the cone,

, andit willbe obvious that therewillbe a greater. radiation of energy fromthe cuter than from the inner surface;

In Fig. 22- however the cone 69 is shallower than that shown in Fig. 21- so that by the time the waves have traveled from the apex 70' to the outer periphery .71 through the material of the cone itself, the

wardly-projecting threaded ends of the armatures as by screws orflotherwise so as completely to enclose the space between the diaphragms and'coil-supporting. spool within.

which the armature gap'is located, so that said gap will be in adust=proof closure.

Having thus described illustrative embodiments of our invention'and methods of obtaining the objects hereinbefore recited withe out however limiting 'ourselves-ther eto,'what we claim-and desire tosecure by Letters Patent is 1. As an improvementin the art of cone venting variable electric currents into -rela:-' tlvely mtense radiated sound waves, the method herein described which consists in I creating a variable magnetic flux by electric currents modified in accordance with sonorous vibrations, superimposing said variable magnetic flux upon a constant magnetic flux without altering the intensity of the latter,

converting the resultant magnetic flux into" two equal and opposite mechanical motions and converting said mechanical motibns-into two sets of substantially-hemispherically-radiating sound-waves of like pressure phase.

radiated waves hai e passed beyond the cone I a cone of the type shown in Fig. 22 is used.

While not limitingourselves to either type of cone or in fact .to a sound-radiating member of any particular shape, we prefer'to employ conical sound-radiating members capale of producing sound waves having wave fronts which are initially curvilinear.

In our -improved sound-radiating device 2. As an improvement in the art of converting variable electric currents into relaf tively intense radiated sound waves, the

method-herein described which consists in creating a variable magnetic flux by electric currents modified in accordance with sono 'rous vibrations, superimposing said variable magnetic flux upon a constant magnetic flux without altering the intensity of the latter,

converting the resultant magnetic flu'x into two equal and opposite'mechanical motions' and converting one of said mechanical modiating sound waves.

it is possibleto adjust and maintain the gap between the armatures with extreme accuracy and the gap length can be made as short approximately as 0.001" when the energizing current is of small amplitude. It is'therefore important in orderto get the benefit of v. suchfine adjustment thatthe length ofthe; gap be uniform over the entire surface of the armature faces, this requiring that said faces be parallel as well as plane. In the present instance thisresult is accomplished by making each armature hollow andhaving its face normal to its axis and thenlassembling'the time into substantially hemispherically ra- 3. A sound radiating devicecomprising in combination, two oppositely-disposed arma-, tures, me ans for magnetiz ng said armatures' by variable electric currents, asupP rt-ing member for each of said armatures, a sound-' radiating member constructed and arranged for the propagation of i'el-atively-intense sound waves through the air, said sound-ra diating member being supported at its center on one of said armatures, and means for pre-- venting interference between the sound waves produced by the two surfaces of said sound radiating member. 1

A sound-radiating device comprising in vibratingsystem on. a close-fitting mandrel combination, two oppositely-disposed armaand adjust ng the several screws 30 whereby tures, means for magnetizing said armature by variable electric currents, a supporting 5. A sound-radiating device comprising in combination, two oppositely-disposed armatures, means for magnetizing said armatures by variable electric currents, a flexible supporting member for each of said armatures, two oppositely-disposed sound-radiating members constructed and arranged for the propagation of relatively-intense sound waves through the air, each said sound-radiating member being supported at its center on one of said armatures; and means for preventing interference between the sound waves produced by the inner surfaces of said sound-radiating members and the sound waves produced by the outer surfaces thereof.

'6. A sound-radiating device comprising in combination, two oppositely-disposed armatures, means for magnetizing said armatur'es by variable electric currents, a flexible sup-' porting member for each of said armatures, two oppositely-disposed conical sound-radiating members constructed'and arranged for the propagation of relatively-intense sound waves through the air, each said soundradiating member being supported at its apex on one of said armatures, and means for preventing interference between the sound waves produced by the inner surfaces of said sound-radiating members and. the sound waves produced by the outersurfaces thereof.

7. A sound-radiating device comprising in combination, two oppositely-disposed armatures, means for magnetizing said armatures by variable electric currents, a flexible supporting member for each of said armatures, a sound-radiating member constructed and arranged for thepropagation of relativelyintense sound waves through the air, said sound-radiating member being supported solely at its center on one of the said armatures, and means for preventing interference between the sound waves produced by the 2 0 surfaces of said sound-radiating mem- 8., A sound-radiating device comprising in combination, two oppositely-disposed armatures, means for magnetizing said armatures by variable electriccurrents, a flexible supporting member for each of said armatures, a conical sound-radiating member constructed and arranged for the propagation of relatively-intense sound waves through the i air, said sound-radiating member being sup ported solely at its apex on one of said armatures, and means for preventing interference the two surfaces of said sound-radiating between the sound waves produced by the two surfaces of said sound-radiating mem-- ber.

combination, two oppositely-disposed armatures, means for magnetizing said armatures by variable electric currents, a flexible supporting member for each of said armatures, two oppositely-disposed sound-radiating members constructed and arranged for the propagation of relatively intense sound waves through the air, each said sound-radiating member being supported solely at its center on one of said armatures, and means for preventing interference between the sound waves produced by the inner surfaces of said sound-radiating members and the sound waves produced by the outer surfaces thereof.

10. A sound-radiating device comprising in combination, two. oppositely-disposed armatures} means for magnetizing said arma- 9. A sound-radiating device comprising in times by variable electric currents, a flexible supporting member for each of said armatures, two oppositely-disposed-conical soundradiating members constructed and arranged for the v propagation of relatively intense 7 matures, means for magnetizing said armatures by variable electric currents, a flexible supporting member for each of said armatures, a conical wave-radiating member constructed and arranged for the propagation of relatively-intense sound waves through the air, said sound-radiating member being supported at its apex on one of said armatures and flaring outwardly from its supporting armature, and means for preventing interference between the sound waves produced by 7 member. I A. 12. A sound-radiating device comprising in combination, two oppositely-disposed ar- -.matures, means'for magnetizing said armatures by variable electric currents, a flexible supporting member for each of said armatures, a conical wave-radiating. member con structed and arranged for the propagation of relatively intense sound waves through the air, said sound-radiating member, being supported solely at its apexon one of said armatures and flaring outwardlyv from its supporting armature, and means for preventing interference between-the sound waves produced by the two surfaces of saidsound-radiating member.

"for the propagation of. relatively intense in combination, two oppositely-disposed arsound waves through the air, each said sound-radiating member being supported at its apex on one of said armatures and flarin outwardly from its supporting armature, an

means for preventing interference between thesound waves produced by the inner surfaces of said sound-radiating members and the sound'waves produced by the outer sur-- faces thereof.

,14. A sound-radiating device comprising matures, means for magnetizing said armatures by variable electric currents, a flexible supporting member for each of said armatures, two oppositely-disposed conical soundradiating members constructed and arranged for the propagation of relatively intense sound waves through the air, each said sound-radiating member being supported solely at its apex on one of said armatures and flaring outwardly fromits supporting armature, and means for preventing interference between the sound waves produced by the inner surfaces of said sound-radiating members and the sound waves produced by the outer surfaces thereof.

15. In a sound-radiating device, a permanent magnet having two oppositely-disposed substantially-rigid arms, two opposite- .ly-disposed and substantially-parallel flexible'permeable members, each attached to one of said arms, twooppositely-directed armatures carried by said members, respectively, the juxtaposed faces of said armatures being separated by a relatively-short gap, and

V ing, a. ermanent magnet vsitelyisposed arms, and two opposite directed armatures supported thereby and arranged for magnetization by said winding, the juxtaposed faces of said armatures being.

means for magnetizing said armatures by variable electric currents. 16. In a sound-'radiati devices, a wlndaving two oppoyseparated by a relatively-short gap and the ma etic leakage path between the poles of sai permanent 'magnet not linking said winding having a reluctance approximately equal to the reluctance of thepath throng said winding.

I 17. Ina sound-radiatingjdevice, a winding, apermanent magnet having two oppositelyisposed arms, two oppositely-directed armatures supported thereby and arrangedfor ma etization by saidwmding, the juxtaposed f iaces rents. V

of said armatures being separated by a relativel -short gap and the mags permanent magnet not linking said winding having a reluctance approximately equal to the reluctance of the path through said winding, and means for varying the reluctance of one of said paths.

18. .In a sound-radiating device, a wind-- ing, a permanent magnet having two oppo sitely-disposed arms,.two oppositely-directed armatures supported, thereby and arranged for magnetization by said winding, the juxtaposed faces of said armatures'being sepa-.

ratedby a relatively-short gap and the magnetic leakage path. between the poles of said" permanent magnet not linking said winding having a reluctance approximately equal to the reluctance of the path through said winding, and means forvarying the separation of "said armatures. v

19. In a sound-radiating device, a permanent magnet having two oppositely-disposed arms, two oppositely-disposed and substantially-parallel flexible permeable members, each attached to one of said. arms, two oppo- 'sitely-directed armatures carried by said members, respectively, the juxtaposed faces of said armatures being-separated by a relatively-short gap, and means for magnetizing said armatures by variable electric currents,

the force exerted on said armatures bythe resultant-of the flux of said permanent magnet and the flux created by the direct current component of said variable'electric currents fora given length of said gap being equal and opposite to the force exerted thereon by said members, and being substantially equal thereto, and opposite, throughout the working rangeof said device whereby for the loweraudible frequencies a maximum change in the length of said gap is eflectedfor a given change in the amplitude of the'variable component of said variable electric cm- 20. In a sound-radiatin device, two oppositely-disposed substantia ly-parallel rigidlysupported flexible members, two oppositelydirected hollow armatures carried. by said of said armatures being separated by a relatively-short gap, and means for magnetizing said armatures by variable electric currents. 21. In a sound-radiating'device, t-wo oppomembers, respectively, the juxtaposed faces sitely-disposed substantially-parallel 'i-igidlysupported flexible members,.two oppositelydirected longitudinally-slotted hollow -armatures carried by said members, respectively,

the juxtaposed faces of said armatures bein separated by a relatively-short gap, an

means for magnetizing said armatures by variable electric currents.

22. In a sound-radiating device, two-oppositely-dispo sedsubstantially-parallel 1" 'dl' supported flexible discs, two opposite y i- I rected armatures carried by said discs, respectively, the juxtaposed faces of. said netic leakage'path etween the poles'ofsaid armatures being separated'by a relatively;

short gap, and means disposed between said discs for magnetizing said armatures by variable electric currents.

23. In a sound-radiating device, two oppositely-disposed substantially-parallel rigldlysupported relatively-stifl flexible discs, two oppositely-directed armatures carried by said discs respectively, the juxtaposed faces of said armatures being separated by a relatively-short gap, and means disposed between said discs for magnetizing said armatures by variable electric currents.

24. in a sound-radiating device, two oppositely-disposed substantially-parallel flexible, discs, two rings arranged, respectively, on the opposite faces of each disc near the periphery thereof, means for clamping each disc between one of the pairs of rings, means rigidly supporting each pair of rings, two oppositely-directed armatures carried by said discs, respectively, the juxtaposed faces of said armatures being separated by a relatively-short gap, and means disposed between said discs for magnetizing said armatures by variable electric currents.

25. In a sound-radiating device, two oppositely-disposed substantially-parallel rigidlysupported flexible members, two oppositelydirected armatures carried by said members, respectively, and having a common axis, the

juxtaposed faces of said armatures being plane and normal to said axis, and being separated by a relatively. short gap, and means disposed between said discs for magnetizing said armatures by variable electrlc currents.

26. In a sound-radiating device two oppositely-disposed substantially-parallel flexible discs, means rigidly supporting each disc at or near its periphery, two oppositely-directed armatures carried by said discs, respectively, the juxtaposed faces of said armatures being separated by a relatively-short gap and means disposed between said discs for magnetizing said armatures by variable electric currents.

27. In a sound-radiating device two oppositely-disposed substantially-parallel rigidlysupported perforated flexible discs, two oppositely-directed armatures carried by said discs, respectively, the juxtaposed faces of said armatures being separated by a relatively-short gap and means disposed be-' tween said discs for magnetizing said armatures by variable electric currents.

In testimony whereof, we have hereunto subscribed our names this 16th day of April,

RICHARD D. FAY. ROBERT E. BEER. 

